A storage tank may include an internal floating roof (“IFR”). Such tanks may be used, for example, to control vapor loss to the environment. Such tanks may be particularly useful for storing volatile products, such as fuel, susceptible to vapor loss. Vapor control may reduce product loss and environmental contamination. An IFR may rise or fall within a tank as product is added or withdrawn from the tank.
Unlike tanks having external floating roofs, a tank having an IFR also comprises a fixed roof to better protect to the IFR from the elements, including lightning strikes, snow and debris. The space between the IFR and fixed roof may collect some product vapors. In some embodiments, a tank may include circulation vents to allow natural ventilation of vapors, thus reducing vapor accumulation and risk of combustion. In other embodiments, product vapors may be released or captured through a pressure-vacuum vent or vapor recovery system.
An IFR may comprise one or more seals around its perimeter to substantially close the gap (“rim space”) between the IFR and tank wall. A seal may comprise a variety of materials and forms, and may comprise a flexible portion, such as a wiper or vapor barrier made of fabric or foam to accommodate variations in rim space, tank wall irregularities, sliding friction and other tank- or product-specific requirements. The flexible portion may comprise a combustible material, such as nitrile, polyurethane or other elastomers or textiles.
The flexible portion may combust if subjected to sufficient heat, such as from a lightning strike, welding or static electricity discharge. Compared to combustion of product vapors, combustion of an IFR seal typically takes a relatively long time. Thus, although vapor reduction may reduce the chance of explosive combustion, combustion of the IFR seal itself remains a risk. However, the relatively long combustion period for IFR seals may allow for detection and combustion control before the product combusts, and preferably before the tank is rendered unusable. For example, if an IFR seal burns, the IFR may become unbalanced, thus allowing it to tip or sink and expose the product to vaporizing and combustion. Or, for large rim gaps, seal combustion may explosively ignite product vapors even if the IFR does not sink or tip.
Because an IFR is contained under a fixed roof and may be generally inaccessible to fire fighters, there exists a need for a method and apparatus useful for extinguishing an IFR seal fire.